The study’s subjects ranged from normal weight to overweight, so cutting back calories did not necessarily translate into severe weight loss; instead, it allowed many subjects to reach a healthier weight. Mark Mattson, a neuroscientist at the National Institutes of Aging, who was not involved in the study, says that it “adds to considerable evidence from animal and human studies that high calorie intake is not only bad for your heart, but it’s bad for your brain.”

Agnes Flöel, lead author of the study, says that most evidence for the benefits of a low-calorie diet in humans comes from long-term epidemiological studies, such as one on an aging population in Okinawa, Japan. But ongoing trials testing the effects of calorie restriction in humans have not yet produced definitive findings. These include the U.S.-government-funded CALERIE study, which follows adults ages 25 to 50 on a calorie-restricted diet. “Animal experiments suggest that both calorie restriction and modified fat intake could be beneficial for the brain,” Flöel says.

The new trial tested reducing total calorie intake, as well as boosting the ratio of unsaturated fat over saturated fat, which is thought to help brain function. A group of 50 healthy older adults with an average age of 60 were divided into three groups: one group was counseled to follow a calorie-restricted diet; another increased the proportion of unsaturated fat over saturated fat in their diets; and the third group had no dietary changes. Flöel says that the subjects in both interventions received dietary counseling and an individualized plan for modifying their diets. Those in the calorie-restricted group were advised to reduce their food intake by about 30 percent without changing the proportions of nutrients in their diet. Subjects reported lowering their typical intake by anywhere from 200 to 1,000 calories per day. Not every person in the calorie-restriction group was able to cut calories by 30 percent, but overall, the subjects in the group lost weight, supporting their own reports that they were eating less.